The link below provides a graphic explaining the number and origins of foreign fighters in Syria. The number of Canadians is noted as 70, with 130 more from the US. The numbers, of course, need to be taken with a grain of salt.
Its hard to say what the impact of these fighters will be on their home countries. There has been a lot of concern that they will return home to carry out terrorist attacks. However, the evidence suggests that the threat of ‘blow-back’ is relatively marginal. According to the Norwegian Defense Research Establishment, the ratio of returning fighters who plan to attack their home countries is between one in twenty and one in one hundred.
The Brookings Institute also just published a fairly sober analysis of the threat of foreign fighters. See Homeward Bound? Don’t Hype the Threat of Returning Jihadists By: Daniel L. Byman and Jeremy Shapiro http://www.brookings.edu/research/articles/2014/09/30-syria-foreign-fighters-byman-shapiro
The biggest impact will likely be in the Middle East, where the political systems are fragile and radical networks are already in place ready to integrate returning jihadists. Tunisia, the most successful of the Arab Spring states has also been one of the largest points of origin with 3,000. That is not good in the long run….